The present invention relates to photoresist patterning. More particularly, the present invention relates to strengthening a photoresist pattern against damage.
Photolithography for patterning photoresist is widely used in the production of semiconductor devices. Presently, 248 nm lithography, using a Krypton Fluoride (KrF) light source, and higher wavelength lithography are very common. It is desirable to perform photolithography with light of a wavelength less than 248 nm to allow a reduction in the design rule to create smaller semiconductor devices. 193 nm lithography using an Argon Fluoride (ArF) light source may be desirable to obtain 0.1 xcexcm to 0.07 xcexcm sizes. 157 nm lithography using a Fluorine (F2) light source may also be desirable.
Chemically amplified positive resists are a type of photoresist that may be used. Amplified positive resists may comprise a polymer with a functional group combined with a separate photoacid generator molecule. Upon exposure to a certain light, the photoacid generator creates a weak acid, which diffuses in the polymer material. After the exposure, photoresist material may be baked, which may cause the acid to attack certain cleavable groups, which deprotects those groups and leaves carboxylic acid in their place. The photoresist layer is then developed by a solvent in a wet bath, which binds to the carboxylic acid, which makes polymers with carboxylic acid groups soluble in the solvent while polymers without the carboxylic acid groups are insoluble in the solvent.
For photoresist materials used for 248 nm and higher wavelength lithography, cross-linking of the photoresist polymer material is typically induced by exposure to deep UV radiation. This method of cross-linking is not effective for photoresist material used in 193 nm and lower wavelength lithography, because these materials are designed to only weakly absorb deep UV radiation. Generally, 193 nm and lower wavelength lithography photoresist material may require the absence of double-bonded carbon and aromatic carbon groups in the polymer. These functional groups have traditionally been used as sites which can be activated to induce cross-linking in photoresist, in some cases by exposure to deep UV radiation, to improve etch and ion implantation resistance. It is believed the absence of these functional groups in 193 nm and lower wavelength photoresist materials, reduces the possibilities for cross-linking these polymers, for example when exposed to deep UV radiation.
Current chemically amplified photoresist material developed for use with 193 nm and lower wavelength lithography may be adversely affected by plasma etching or ion implantation. Exposure of a 193 nm or lower wavelength photoresist film to an etch plasma may lead to a roughening of the film surface and a resulting degradation of the pattern quality. Striations in the walls of trenches and vias, an increase or decrease in critical dimensions, distortion of feature shapes, and pinhole etching of dielectric beneath photoresist film may be some of the undesirable outcomes of this degradation. The release of functional groups during plasma processing may occur from the bulk of the photoresist layer, which may significantly modify the plasma and may affect the etch chemistry. The release of these functional groups may also cause some of the above-described roughening of the film. Photoresists designed for 193 nm and lower wavelength lithography may also be etched at higher rates, compared to established photoresist materials.
The 193 nm and lower wavelength lithography photoresist film may also be degraded during the ion implantation process, due to direct interaction of ions or heating of the photoresist film. Typical high-throughput conditions for ion implantation result in significant wafer heating, which may cause thermally induced reticulation or roughening of the photoresist film and degradation of the photoresist pattern quality. Degradation of the photoresist pattern quality during implantation can lead to several undesirable outcomes, including poor CD (critical dimension) control of the implanted region, reduction in the absolute dosage, and modification of the ion depth profile.
For 193 nm photoresists, electron-beam conditioning has been used in an attempt to improve etch performance, It is believed that this electron-beam conditioning may cleave functional groups of the polymer making the photoresist, which may make a more stable photoresist layer but may also lead to significant shrinkage of the film as these functional groups exit the photoresist film as small molecules. Although the removal of these groups may reduce the subsequent reactivity of the film under plasma conditions, the shrinkage can lead to undesirable and poorly controlled shifts in the critical dimension of features. In addition, it is believed that this electron-beam conditioning may cause chain scission, which could degrade the overall strength of the material and act as an undesirable side-effect of the conditioning. In addition, it is believed that, although electron-beam conditioning may reduce subsequent photoresist damage, the control of the electron-beam induced changes in critical dimensions may not be repeatable enough to provide consistency for a large scale production of semiconductor devices. In addition, electron beam conditioning may require subjecting a wafer to a process that may not be part of a normal chip fabrication process and that may require an unusually long period of time, which may require the use of additional equipment not normally used in a chip fabrication process and a longer processing time.
In view of the foregoing, it is desirable to provide a photoresist film for 193 nm and lower wavelength lithography that is more resistant to damage caused by plasma etching and ion implantation, is less susceptible to shrinkage, and is etched at a reduced rate.
To achieve the foregoing and in accordance with the purpose of the present invention a method for creating semiconductor devices is provided. A photoresist layer is provided on a wafer. The photoresist layer is patterned. Polymers in the patterned photoresist layer are chemically cross-linked by exposure to at least one reactive chemical. The pattern in the photoresist layer is transferred to the wafer.
In another embodiment of the invention, a method for creating semiconductor devices is provided. A photoresist layer on a wafer is provided. The photoresist layer is patterned comprising exposing regions of the photoresist layer with a light with a wavelength no greater than 193 nm, and removing regions of the photoresist layer. Polymers in the patterned photoresist layer are cross-linked. The pattern in the photoresist layer is transferred to the wafer.
In another embodiment of the invention, a method for creating semiconductor devices is provided. A photoresist layer on a wafer is provided. The photoresist layer is patterned, comprising exposing regions of the photoresist layer with a light with a wavelength no greater than 193 nm, and removing regions of the photoresist layer. The wafer is heated. Polymers in the patterned photoresist layer are chemically cross-linked by exposing the patterned photoresist layer to a reactive gas. The pattern in the photoresist layer is etched into the wafer.
In another embodiment of the invention, a semiconductor device is created. A photoresist layer is provided on a wafer. The photoresist layer is patterned. Polymers in the patterned photoresist layer are chemically cross-linked by exposure to at least one reactive chemical. The pattern in the photoresist layer is transferred to the wafer.
In another embodiment of the invention, a reaction chamber for processing a wafer with a patterned layer of photoresist material, wherein the photoresist material was patterned by exposing the photoresist material using light of a wavelength less than 248 nm is provided. A chamber is provided with a central cavity. A wafer support for supporting the wafer in the central cavity is provided. A cross-linking reactive chemical source in fluid contact with the chamber and which provides a reactive chemical which causes cross-linking of the photoresist is provided.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.